A printed circuit board handle is normally constructed as a simple aluminum extrusion and it generally serves several purposes. Its primary purpose is to provide a means for grasping the printed circuit board and thereby facilitate its insertion into and removal from electronic equipment. However, since printed circuit boards are typically wave soldered they can reach temperatures of 500 degrees Fahrenheit during that process. Therefore, another primary purpose of the printed circuit board handle is to provide a means of stiffening the printed circuit board in order to prevent it from warping in the high temperatures of the wave soldering process. Another subsidiary purpose of the printed circuit board handle is one of identification, since identifying markings, including bar code labels, are often placed on it.
Printed circuit boards are preheated before they are subjected to the high temperatures of the wave soldering process. Because of such preheating and the prevalent use of aggressive fluxes, the flux would often penetrate into and become entrapped in the area between the handle and the printed circuit board. After a few days time, moisture absorption by such entrapped flux would progress to the point of causing the entrapped flux to "bubble" out from between the handle and the printed circuit board. The flux bubbles must then be manually cleaned out using a brush and locally applied solvents. Even after cleaning, bubbles may reappear. The cleaning operation will then have to be repeated.
Alternatively, the printed circuit board can be baked prior to cleaning in order to accelerate the moisture absorption chemical reaction to completion and thereby preclude the need for repetitive cleaning due to prolonged bubbling. However, these baking, cleaning and retesting operations are expensive in terms of labor, inventory and scheduling disruption.
Other methods of cleaning, such as vapor degreasing, which comprises an aggressive spraying directed into the problem area, and spray over immersion, have also proven to be ineffective means of removal of entrapped flux.
Alternative mechanical approaches to remove entrapped flux included the use of dimples on the printed circuit board side of the handle's flange, but that approach was also unsuccessful. Another mechanical approach involved the use of Kapton tape over the crevice where flux excursion begins. While this method worked, its cost was prohibitive.
Accordingly, it is the object of the present invention to provide a novel printed circuit board handle which inhibits flux entrapment to such an extent that there is no need for baking, and only one conventional cleaning operation is required after the wave soldering process to remove entrapped flux.